This invention relates to microwave orthomode transducers for concurrent transmission of electromagnetic signals of differing polarizations and, more particularly, to an orthomode transducer having a straight port communicating with a circular waveguide section via a tapered transition, a side port communicating via a window with the circular waveguide section, and a system of blade-shaped cross-polarization suppressors allowing for increased bandwidth.
Orthomode transducers are widely used in communication systems, including satellite communication systems, because of their capacity to provide for a concurrent transmission of signals of differing frequencies and differing polarizations through a common microwave port suitable for connection to antenna or other device. In a typical construction of orthomode transducer, the transducer includes a waveguide section of circular cross section having an output port which may be coupled to an antenna, by way of example, and further comprising two waveguides of rectangular cross-sectional configuration communicating with the circular waveguide section. The two rectangular waveguides serve as input ports to the transducer, and are arranged relative to each other for applying two electromagnetic waves of linear polarization to the circular waveguide wherein the polarization from the first rectangular waveguide is perpendicular, or orthogonal, to the polarization from the second rectangular waveguide. The transducer operates in reciprocal fashion such that the output port may receive plural signals from an antenna wherein signals of one polarization are coupled to the first rectangular waveguide and signals of an orthogonal polarization are coupled to the second rectangular waveguide. The signals may be provided at different carrier frequencies, such as up-link and down-link signals between a satellite and the earth. Alternatively, signals of the two rectangular waveguides may be provided at a common frequency in which case the orthogonally polarized waves combine in the circular waveguide section to provide a single output signal having either a linear, elliptical, or circular polarization depending on the relative magnitudes and phases of the signals in the two rectangular waveguides.
A problem arises in that presently available orthomode transducers are limited in the bandwidth of signals that can be coupled between the rectangular waveguides and the circular waveguide section. This, in turn, provides a limitation upon the spectral content of signals to be communicated via the transducer in a communication system. Also, in satellite communication systems, an overly large physical size of the transducer may provide difficulties in the packaging of microwave equipment to be carried by the satellite. Thus, there is a need to increase the bandwidth of orthomode transducers, as well as to decrease the physical size.